1. Field of the Invention
The present invention relates to high efficiency gas burning fireplaces. More particularly, the present invention relates to a prefabricated fireplace designed to be mass produced and used at various levels of thermal efficiency while maintaining an optimum burner efficiency.
2. Description of the Prior Art
Heretofore, prior art gas burning fireplaces were designed to burn fuel at one or more fixed burn rates, only one of which was set for highest burner efficiency at the factory Several important factors that determine burner efficiency are fuel to air ratio, the temperature in the combustion chamber and the time the mixture is allowed to burn before being exhausted from the fireplace.
Our U.S. Pat. No. 4,793,322 shows and describe a direct vented gas fireplace which has a high thermal efficiency and an optimum fuel to air mixture which result in very low emission of CO and NO.sub.x. The heat produced in the combustion chamber is sufficient to create hot exhaust gases that are directed through a relatively short exhaust passageway which terminates in a short horizontal exhaust stack. The exhaust gases generate a suction on the combustion chamber which draws fresh air for combustion into the combustion chamber. Once the combustion air inlets are designed for an optimum burn rate, the system will maintain a very efficient burn rate over a range of gas burning rates so long as the combustion chamber maintains a high combustion temperature and nothing is done which would change the differential pressure drop across the combustion chamber. It is well known that lengthening the exhaust passageway and exhaust stack and/or lengthening the intake passageway used to supply fresh combustion air will change the differential pressure drop across the combustion chamber, thus, will also change and effect the optimum burner efficiency and the thermal efficiency of the fireplace system.
Our U.S. Pat. No. 5,016,609 shows and describes another zero clearance fireplace which was designed to provide an efficient gas burner system in a fireplace having up to three airtight glass sidewalls and also provide an efficient heating system for rooms and/or small apartments or condominiums. Once the inlets and outlets to and from the combustion chamber were fixed, there was no provision to further fine tune the optimum burner efficiency in the field.
When zero clearance fireplaces of the type shown in the above mentioned prior art patents are placed in intake and/or exhaust environments other than substantially the exact environment for which they were designed and/or calibrated, the optimum burner efficiency is affected as a result of the field environment.
When a prefabricated fireplace is designed for its highest possible heating efficiency it is provided with a forced air fan in the heat exchanger and the heat exchanger system is designed for a high recovery of heat from the exhaust gases before they are released to the atmosphere. A high recovery heat exchanger can add substantially to the cost of a prefabricated fireplace. Such cost may easily be justified in locations which have a very high degree-day heating season, but is not easily justified in low degree day parts of the world such as California, the south and southwest and areas that have a mediterranean climate.
People living in such warm climate areas may desire a prefabricated fireplace with a decorative gas burner log system and may not desire air tight glass side walls, but may desire a more realistic wood burning fireplace effect that is presented by glass panel doors that have handles and may be physically opened.
Most prefabricated fireplaces are either purchased by architects/designers for their clients or are sold through distributor/installers that have a very high degree of sophistication concerning both cost and thermal efficiency.
It would be desirable to provide such sophisticated customers with a single base fireplace unit having up to three fixed glass side walls or glass doors which could be fitted with a standard heat exchanger, or a blower heat exchanger or a very high efficiency blower heat exchanger for different intake and exhaust conditions that effect burner efficiency. It would be highly desirable to provide the sophisticated installer with one simple adjustment which would enable setting an optimum burner efficiency after field installation.